3.4. The CSS Platform

The type
attribute of the <style> tag is where you
specify the language and syntax you'll be using for
your style sheets. This value is in the form of a content-type
declaration, and the CSS specification declares
text/css as its preferred content type. By
convention, today's browsers treat
text/css as the default type, but the
<style> tag's
type attribute is required in the HTML 4
recommendation. Therefore, always specify the type
attribute for all <style> tags. A
style element that relies on the CSS syntax should
look like the following:

<style type="text/css">
...
</style>

For trivia buffs, Navigator 4 (only) featured a short-lived
alternative syntax that followed the JavaScript object reference
format. This alternate type, text/javascript,
provided JavaScript equivalents for most of the style attributes and
structures provided by the text/css syntax.